1. Field of the Invention
The present invention relates to a piston for an internal combustion engine with a piston head and a piston skirt, which performs a sliding reciprocating motion in a cylinder, the piston skirt comprising at least one bearing surface. The present invention further relates to a method of producing such a piston.
2. The Prior Art
Known internal combustion engines for motor vehicles comprise, in addition to other components, an engine block with one or more cylinders and cylinder heads associated therewith together with pistons which perform reciprocating motion in the cylinders. The pistons comprise a piston head and an adjoining piston skirt. In the area of the piston skirt there is provided a bore for receiving a piston pin mounted therein, on which there is seated a connecting rod connected with a crankshaft.
Although the piston performs a straight downwards movement in the cylinder as a result of the combustion pressure exerted by the ignited petrol mixture or the diesel fuel, the piston is also subject at the same time to a sideways movement as a result of the circular motion of the connecting rod on the crankshaft and the clearance between the piston and the cylinder. During the reciprocating motion of the piston, this sideways movement causes friction to arise between the bearing surface of the piston skirt and the internal wall of the cylinder. In order to keep this friction between the piston and the cylinder resulting from the movement of metal on metal as low as possible, a lubricating film, e.g. oil, is produced between the bearing surface of the piston and the internal wall of the cylinder. At the elevated temperatures arising in an internal combustion engine, the lubricating film may rapidly lose its effect, resulting in inadequate lubrication and consequently impairment of the sliding properties of the piston.
This disadvantage has led to coating of the bearing surface of the piston skirt with an overlay which is abrasion resistant and exhibits a low coefficient of friction. It is additionally known to provide recesses or grooves in this overlay, in which additional lubricant, such as oil for example, may be introduced and collected. A known piston of this type is described in detail in international patent application WO 2005/042953 A2.